The major objectives of this project are: (1) To study the effects of immunosuppression on the pathogenesis of experimental viral infections which have the ability to involve the central nervous system (CNS); (2) To use the immunosuppressed virus-infected animal as a recipient of adoptively-transferred lymphoid cells or serum from syngeneic virus-immune donors in an attempt to assess the relative contributions of the cellular and humoral immune responses to the outcome of infection; (3) To correlate these in vivo observations with functional activities which can be quantitated in vitro, particularly T cell-mediated cytotoxicity; (4) To define the conditions in which certain viral infections preferentially lead to the induction of virus-specific cytotoxic T cells (CTC), and (5) To determine the mechanism(s) by which specific and non-specific immune stimulation induces the recall of these CTC in previously infected animals having long-lived virus-specific T cell memory.